Electric Bike Glossary
Electric bike terms and definitions
For many people an electric bike introduces us to a whole new world of terminology. Such terms as voltage, wattage, and amperage may sound like a foreign language. Keep reading if you want to learn more about the true details of what makes an electric bike an electric bike.
The Schwinn Power Pac 29.4-volt 10 Amp-Hour lithium polymer battery has about 5 times the power to weight ratio (specific energy) as lead acid, 4 times nickel cadmium, 2.5 times nickel metal hydride or 1.4 times the power to weight ratio of lithium ion. This means more power for the same weight or the same power in a much lighter smaller space, or a combination of increased power and less weight.
Voltage can be thought of as the pressure or strength of electric power. Imagine fuel flowing through a pipe with higher or lower pressure (voltage). The Schwinn Power Pac has a peak voltage of 29.4 volts. And a cutoff voltage about 23 volts where the power management card inside the battery pack shuts down the system to protect it from over discharge. This greatly extends the battery life.
Amps or Ampere
Amperage or amps can be thought of as the volume or quantity of electric power, or how much fuel is flowing through the pipe. Amps are measured in current load. Climbing a hill will cause the motor to draw more current load or ìampsî to maintain the same bike speed. The maximum amps the Schwinn Plug N' Drive motor controller will allow the motor to draw through the system is 15 amps, with the average current draw about 6.5 amps. The amps used by the hub motor vary widely according to rider weight, terrain, road conditions, desired speed, wind and amount of effort the rider contributes so the total run time of the battery also varies widely from 30-40 minutes under primarily electric power to 90 minutes or more depending on the power contribution of the cyclist.
A unit of electrical current equal to 1 amp discharged continuously over 1 hour. A 10 Amp-Hour (10Ah) battery can supply, for example, 5 amps for 2 hours or 6.5 amps for about 1.5 hours
A unit of work or power that is the product of voltage multiplied by amps.
28 volts X 6.43 amps = 180 watts
746 watts = 1 horsepower
A bicyclist setting a world speed record for 1 hour needs to maintain about 475 watts. The occasional recreational cyclist can maintain about 1/10th of a horsepower or 75 watts for 1 hour with bursts of 200 watts for a few minutes, more or less depending on the riders conditioning. The Schwinn Plug N' Drive motor more than doubles the recreational cyclists input with 150 watts of continuous power and 250 watts of momentary power to help get the recreational cyclist through the tough parts of the ride.
A unit of electrical energy equal to one watt of power for one hour
The Watt-Hours of a 29.4 volt 10 amp hour battery is 29.4 X 10 = 294 Watt-Hours in a Schwinn Power Pac.
Peak Watts Vs Nominal Continuous Watts
Peak Watts: The Schwinn Plug N' Drive motor is designed to draw a peak load of 290 watts. Peak watts are calculated by multiplying the nominal motor amp draw (10) by the peak voltage (29) however, the motor can only sustain the peak output for a few moments before the speed controlling circuitry backs down the voltage to ensure a longer motor service life. Under certain situations the wattage can go even higher, but this happens rarely and is seldom used to rate motors.
Nominal Continuous Watts: This is the output that the engineers designed as optimal for maximum efficiency and durability. The high efficiency Schwinn Plug N' Drive motor is rated at nominal continuous output of 150 Watts of mechanical work.
Watt's the difference?
A watt is a unit of power or work. But electrical and mechanical watts are a bit different. When the cyclist wants to maintain a speed of 16.5 MPH on a flat paved road with no additional wind resistance, this requires about 125 watts of mechanical work. If the bikes electrical motor provides all the power to maintain this speed, the motor must produce a mechanical output of 125 watts. The Schwinn Plug-n-Ride hub motor system is designed to be very efficient at about 80% (some competitors are less than 50% efficient). The electrical watts supplied to the motor need to be about 150 watts to produce 125 mechanical watts at 80% efficiency. This would draw about 5.2 amps at 29 volts through the Schwinn Plug N' Drive electrical system.
A watt is a measurement of work or power. But not necessarily a reliable way to compare competitors motors. An electrical motor is usually rated by the nominal continuous mechanical work output. Some motors are rated using the higher electrical input, or even the peak electrical input, even if the system will not support it.
An inefficient 400 watt bicycle motor system may not accelerate as fast as an efficient 200 watt bicycle motor system. Power can be wasted in many ways such as mechanical drag and heat, neither get power to the ground. A good example of modern technology creating efficiencies is the light bulb, also measured in watts. A 13 watt compact fluorescent light bulb can create the same amount of light or lumens as a 55 watt standard light bulb. The standard light bulb wastes 42 watts, or over 75% of the energy it consumes, as unnecessary heat.
Likewise, if a bicycle motor system is noisy or if there are added belts, gears or chains to link the motor to the bicycles drive train, there is probably mechanical drag wasting energy.
Excess system weight can quickly add up to require more power just to move the bike down the road, this can be a big waste of energy, both electrical and yours!
And, if a motor gets hot to the touch it's not operating efficiently and wasting electrical energy as heat. Poor quality bearings and motor materials, sloppy manufacturing tolerances, internal buildups of brush dust and mechanical drag from brush-type systems all draw more amps, increasing the watt listing but not getting power to the ground.